This application relates generally to climate control (heating, ventilating and air-conditioning, or HVAC) systems, especially to those used for motor vehicles, and more specifically to motor actuators therefor and electric motors for such actuators.
Climate control systems, particularly those for motor vehicles, normally include air passages having movable dampers therein to control airflow through the passages. The movable dampers are usually moved by hand-manipulating hand-controlled elements. In this respect, an operator manipulates one of the hand-controlled elements to move one or more of the dampers to a respective desired position for achieving a desired airflow pattern in the passage(s). In the past, the hand-controlled elements have been coupled with the dampers in various ways for moving the dampers. For example, hand-controlled elements have been directly attached to the dampers by cables so that when the hand-controlled elements are manipulated the cables move the dampers. In other systems, hand-controlled elements have controlled vacuums, for applying the vacuums to move dampers.
More recently, dampers have been moved by small electric motors at the dampers, with electrical signals being sent to the electric motors in response to manipulation of the hand-controlled elements. In this respect, some such motors have been packaged as motor-actuator components, each motor-actuator including at least a motor and gears for achieving a desired mechanical advantage between the motor and its associated damper.
A problem that arises from use of electric motors for changing positions of dampers is that the motors do not automatically stop when their dampers reach desired positions set by the hand-controlled elements. Thus, additional electronic and/or mechanical devices must be provided for assuring that the power signals are turned off once associated dampers reach desired positions.
A simplified version of one such prior-art system for moving a damper 10 is depicted in FIG. 2. In this prior-art system, a motor actuator 16 includes, in addition to a motor 12 and gears 14, a rheostat-type (or potentiometer-type) component 18 that is represented in FIG. 2 by a simple potentiometer. Examples of similar such systems are disclosed in U.S. Pat. No. 4,795,867 to Ohi et al. and U.S. Pat. No. 4,877,926 to Yamase. In any event, in the simplified system of FIG. 2, as the motor 12 moves the damper 10 via the gears 14, the gears, or some linkage to the gears, also moves one or more brushes 20 of the potentiometer 18 to provide feedback to a motor control unit (MCU) 22 of a control head 24. The MCU 22 compares this feedback 21 with positions of hand-controlled elements 26 to determine when a motor driver 28 should discontinue sending power signals for driving the DC electric motor 12. Such a system as is depicted in FIG. 2 is sometimes referred to as a five-pin potentiometer feedback system because it involves five terminals for the motor actuator: two power terminals for receiving the motor-driving power signals 29, and three terminals for the rheostat-type component 18 (which requires a ground wire 30, a power voltage wire 32, and a feedback wire 21). A similar system might also be carried out as a four-terminal system, although it would have to be arranged differently than shown in FIG. 2.
Systems like that of FIG. 2 have several drawbacks. One problem is that each motor actuator must include a rheostat-type, or potentiometer-type, component, which makes the motor actuator unduly expensive. Further, such a system often requires five wires between the control head and the motor actuator, again increasing complexity and adding to expenses.
Such an electric-motor system as shown in FIG. 2 has the benefit that it provides an absolute position feedback, an initial full-range calibration is required for each motor actuator so that the motor control unit (MCU) 22 can learn all angular positions of the damper 10 corresponding to feedback signals on the line 21.
More recently, a different electric-motor system has been employed for automotive HVAC systems, namely, a back EMF pulse count system as depicted in FIG. 3. In this system, a control head 33 includes a back EMF pulse counter 34 that counts back EMF pulses on power-signal lines 29 that automatically arise when the motor driver 28 drives the motor 12. A count of these back EMF pulses provides an indication of motor shaft rotation and, therefore, movement of the damper 10. In theory, if an MCU 36 of the control head 33 is calibrated to know an end position of the damper 10, for example a position when the damper 10 completely closes an air passage, then it will also know other positions of the damper 10 corresponding to particular counts of back EMF pulses away from the end position. This system has the benefit of eliminating the rheostat-type component 18 and reducing the number of terminals and wires.
However, the system of FIG. 3 suffers from a number of other disadvantages. One problem is that the back EMF pulse counter 34 is a rather complicated and specialized device that must be manufactured by a specialized manufacturer. Further, the accuracy of such a back EMF pulse counter 34 is adversely affected by the erratic nature of back EMF. In addition, the wearing of motor power brushes, and varying torque loads, can adversely affect a back EMF pulse count. Similarly, starting and stopping transients can cause improper counts. Thus, even though this system reduces the cost of the motor actuator by eliminating the rheostat-type component 18, it increases the cost of the control head by requiring a highly specialized back EMF pulse counter 34. Similarly, this system requires an additional particular supplier for providing the specialized EMF pulse counter. Further, this system is often prone, over time, to get out of calibration as mistakes are introduced into its back EMF pulse count.
Thus, it is an object of this invention to provide a climate control (HVAC) system that includes relatively inexpensive and uncomplicated motor actuators having reduced numbers of terminals and wire connections. At the same time, it is an object of this invention to provide a motor actuator that provides position feedback to an MCU that is reliable under all load and wear conditions and that can be evaluated by the MCU without the use of an expensive, complicated, component that must be manufactured by a specialized manufacturer. Similarly, it is an object of this invention to provide a motor with built-in feedback that can be used in such a motor actuator and/or otherwise.